1. Field of the Invention
The present invention relates to an apparatus and method for packing gravel within the bore of a subterranean well.
2. Description of the Prior Art
Of considerable magnitude in the production of hydrocarbons such as oil and gas from a producing well is the problem of sand flow into the well bore from unconsolidated formation. Production of sand with the flow of hydrocarbons will cause the well bore to gradually fill up with minute sand particles until production perforations in the casing and, oftentimes, the end of production tubing inserted therein are covered, resulting in a significant reduction in fluid production. In many instances, sand production will cause the well to die.
In addition to reduction of fluid production, flow of sand also may cause severe damage to equipment such as pumps, chokes and the like. In flowing wells, fluid velocity may be sufficient to scavenge sand within the well bore and produce it with the fluid hydrocarbon, resulting in holes being cut in the tubing and flow lines.
One well known means of controlling flow of sand into the well bore is the placement of gravel on the exterior of a slotted liner to filter sand produced with the oil or gas and thus prevent its entry into production tubing. The slotted liner or screen must be designed to prevent entry of the gravel itself into the production tubing.
The reverse circulation method of packing gravel provides for pumping the gravel down the well in the annulus between the production tubing and the well casing. The gravel is deposited on the outer periphery of the screen assembly while the fluid returns to the top of the well through the production tubing. A pressure buildup is noted at the surface and fluid pumping stopped when the gravel covers the screen. After gravel settlement, the tubing is disconnected from the screen assembly and pulled out of the hole.
Although other fluids have been used, treated and filtered production or nearby well or surface water is preferably used in most gravel packing processes during the cleaning and washing procedure. The water is treated to remove contaminants such as cement particles, scale, and other foreign material generally resulting from the circulation of water in the well bore. Because the volume in the annulus between the production tubing and the well casing may be as much as eight to 10 times greater than the volume of the production tubing, considerably more water must be used and thus treated and filtered if clean fluid is to be used in a reverse circulation process or method than is used in conventional wash down methods.
In order to provide a gravel pack apparatus which is more efficient than prior art apparatuses and, primarily, to drastically reduce the amount of fluid which must be used during a gravel packing process, crossover equipment has been developed for use with screen assemblies and high performance packers. Such equipment now has made it feasible to gravel pack using only a fraction of the volume of fluid heretofore utilized because the fluid is maintained within the tubing and is circulated only within the treatment zone which is isolated by the packing element of the packer.
Although such an apparatus has provided many advantages over the use of conventional prior art techniques, heretofore its use has been confining because it has not been able to be successfully utilized in high pressure wells which require the use of high density fluids, such as highly weighted muds instead of water. Heretofore, if such an apparatus were utilized in conjunction with the mud system, the screen as well as the gravel pack would become plugged, resulting in a severe limitation of hydrocarbon production therethrough.
It is, therefore, an object of the present invention to provide an apparatus and method for gravel packing utilizing concentric strings of tubing wherein the zone being gravel packed is completely isolated from the well control fluid (mud) during the gravel pack operation and may remain isolated from it, if desired, after completion of the gravel pack operation.
It is also an object of the present invention to provide an apparatus and a method which utilizes a crossover assembly with concentric strings of tubing to eliminate the necessity of pumping gravel in a high pressure well down the tubing-to-tubing annulus.
It is a further object of the present invention to provide an apparatus and method whereby flow paths into, through, and around a gravel pack screen can be altered and regulated by longitudinal manipulation of an internal tubing string within an outer tubing string.
It is a further object of the present invention to provide an apparatus and method for gravel packing wherein high pressures may be utilized during acidizing and squeezing of gravel into the formation.
Other objects of the present invention will be readily apparent from a reading of the Figures, the specification below, and the claims.